The present invention relates to a semiconductor device with an improved wiring structure.
Aluminum, which is generally used as a wiring metal for semiconductor devices, has defects such as disconnections due to electromigration caused when the pattern of a wiring metal layer is made very fine or disappearance of the junction due to an extraneous process of alloying between Al and the Si substrate caused when the diffusion layer in a semiconductor substrate (e.g. silicon substrate) is shallow. However, the most serious defect is the problem of corrosion. Corrosion is caused by the gradual chemical or electrical corrosion of the Al wiring due to the presence of water which has been unavoidably trapped inside during the manufacture of the semiconductor device or which has entered from outside the package when the semiconductor device is rendered conductive in a general manner.
In order to solve this problem, it has been conventionally proposed to form a passivation film consisting of phosphor doped glass (PSG) on the Al wiring so as to prevent water from entering the Al wiring area from the outside and to facilitate the elimination of corrosion of the Al wiring. However, the formation of PSG requires a temperature of about 400.degree. C. Due to this heat, a number of hillocks (projections) are formed on the Al wiring, and these hillocks other cause the generation of pinholes and cracks, thus disabling the function of the passivation film. Further, PSG itself absorbs humidity easily and generates a small amount of phosphoric acid, thus adversely facilitating the corrosion of the Al wiring which is in contact with the PSG.